The present invention relates to a method of manufacturing a battery comprising a step of forming an electrolyte layer coated with electrolyte onto an electrode.
Recently, portable electric equipment has been developed, hence, a battery has an important role as an electric source of such portable electric equipment. The portable electric equipment is required to be miniature and lightweight, in response to this request, the battery is also requested to be miniature in accord with accommodating space inside the portable electric equipment, and to be lightweight in order not to increase weight of the portable electric equipment as possible.
As the battery responding to such a request, in replace of a lead-acid battery and a nickel-cadmium battery, which are used to be the mainstream in the secondary battery, a lithium secondary battery and a lithium ion secondary battery whose energy density and output density are higher than that of these batteries, are expected.
Conventionally, in the lithium secondary battery or the lithium ion secondary battery, liquid-type electrolyte, which is dissolved lithium ion in nonaqueous solvents, is employed as a material working for ion conduct (hereinafter, it is called as to electrolyte liquid). With this reason, a package must be made of a metal case for preventing leakage and strictly maintain hermeticity inside the battery. However, with the metal case employing as the package, it is extremely difficult to produce a battery such as a sheet-like battery, which is thin and large, a card-like battery, which is thin and small, or a battery, which is flexible and freer in shape.
In replace of the electrolyte liquid, it is therefore suggested that a secondary battery is employed electrolyte such as gel-type electrolyte, which macromolecular compounds has electrolyte liquid including lithium salts, solid-type electrolyte, in which lithium salts are diffused to macromolecular compounds having ion conductivity, or electrolyte, in which a solid-type inorganic conductor has lithium salts. In these batteries are free from leakage, so that the metal case is unnecessary as a package. This can be gained miniaturization, reduction in weight and in thickness of the battery by using a laminate film and the like as a package material, which results in a battery flexible in shape.
In the case of employing the gel-type electrolyte and the like, for instance, electrolyte layers are formed on electrode mixture layers formed on an electrode collector by means of a method described later. First, as shown in FIGS. 1A and 1B, a plurality of electrode mixture layers 126 is intermittently formed on a belt-shaped electrode collector 125a to form a belt-shaped electrode 121a, and the belt-shaped electrode 121a is impregnated into an unillustrated tank accommodating the electrolyte. Next, the belt-shaped electrode 121a is pulled up from the tank, and scraped the electrolyte adhering to its both faces, which forms electrolyte layers 123 with a predetermined thickness on the both faces of the belt-shaped electrode 121a. Following this, the electrolyte of the electrolyte layers 123 are dried and the belt-shaped electrode 121a formed the electrolyte layers 123 thereon is rolled with a separating paper. After this, the rolled electrode 121a is cut between the electrode mixture layers 126 so as to make a plurality of electrodes. In connection with this, as for the reason that the belt-shaped electrode 121a is rolled with the separating paper, it prevents that solvents in the electrolyte evaporates or the electrolyte layers 123 are absorbed the water. FIG. 1B is a view in response to a cross sectional structure corresponding to a IB—IB line in FIG. 1A.
In the above-mentioned method, for the reason that the electrolyte layers 123 are formed by impregnating the belt-shaped electrode 121a into the tank, the electrolyte directly adheres on the belt-shaped electrode collector 125a even in regions where the electrode mixture layers 126 are unformed. However, an electrode terminal, which connects the electrode collector to an external terminal, needs to be attached in the regions, for this reason, as shown in FIGS. 2A and 2B, the electrolyte adhering on the region where the electrode terminal is attached must be stripped.
When stripping the electrolyte, the separating paper is necessary to be stripped temporally, which the solvents in the electrolyte evaporate. This causes voltage failure and capacity failure of the battery.
Further, in the case that the electrode mixture layers 126 are formed onto the both faces of the belt-shaped electrode corrector 125a, if regions where the electrode mixture layers 126 are formed, are different in a surface and a back of the belt-shaped electrode corrector, a thickness of the belt-shaped electrode 121a becomes various depending on regions. For this reason, the electrolyte layers 123 are difficult to achieve its evenness by means of a method of scrapping with a scoop.